The best scene of tonight’s episode of “The Walking Dead,” didn’t involve zombies, or bullets, or blood, or even dialogue for that matter. While disease, death and mayhem are taking over other parts of the former West Georgia Correctional Facility, one character delivers a surprisingly tender, painful insight into her past.

It’s another example of the show’s ability this year to contrast the big, set-piece zombie attacks with small, intimate stories that really illustrate the human toll of this horror story, and it shows off the depth of storytelling that’s being presented this year. (You hear that, Emmy people?)

“Infected” explores not just life and death – that’s pretty much a constant theme in a zombie show – but the tenuous relationships between the living and the dying, between a father and his daughters, between two survivors in love (or something like it), between a mother and the child she still grieves over, and even between, yes, a farmer and his pigs.

There were mysteries explained, like why Rick Grimes really gave up his leadership role, and new, disturbing ones presented, as a violent sickness rips through the prison. But that’s not the only danger: there’s somebody behind the fence who means the community grievous harm as well.

Tonight’s episode picks up essentially where last week’s premiere left off. Patrick, the young, nerdy boy with the black-framed glasses, has died, and come back a walker. Having died in the showers of cell block D, he wanders back to the living quarters, to feast on a sleeping, and snoring, resident. Soon enough, there will be a major, deadly outbreak in the block, of both whatever killed Patrick, and zombies.

That’s not the only threat in the prison. The episode opens on the fence, under a full moon, and somebody is feeding mice to the walkers, drawing more and more of them to the fence. Before the episode is over, this mysterious malcontent, or malcontents, will gruesomely burn two people to death.

But before that, dawn breaks on the prison. While zombified Patrick is gnawing away at a leisurely pace on the insides of his victim, Rick wakes up his son, Carl, to go and tend to the pigs. Carl mentions there’s been a build-up of walkers along the fence, and suggests they help the clearing crew. Rick says they’ve got other plans. “Dad,” Carl says quietly, “when can I have my gun back?”

Ding, ding, ding! If you were wondering why Rick really gave up everything to tend to pigs and crops, now you know. It wasn’t about himself at all; rather, he was trying to save his son from losing what remained of his own humanity.

(For the record, we will reiterate what we said last season: speaking strictly within the universe of the zombie apocalypse, Carl was totally justified in shooting that boy from the Governor’s gang. Did we learn nothing from the Randall incident?)

Rick and Carl are tending to the pigs, and Michonne has just left the gates on horseback when they all hear muffled gunshots coming from inside. What zombie-Patrick started has now become a fully blown zombie outbreak inside cell block D. It’s wonderfully graphic: Patrick’s first victim rolls out bed a walker, and his intestines just slide out of his body.

Glenn, Daryl, Rick, and Carol run in to help. Ryan, who we briefly saw last week at story/self-defense time with Carol, gets bit on the forearm, and Carol prepares to cut his arm off, before realizing he was bit on the neck, too.

There follows a sequence with Ryan and his two daughters, Lizzy and Mika, and it’s impressive how much emotion they manage to draw out of characters we hardly know. Carol brings the daughters in to say goodbye, after promising Ryan she’ll look after them as if they were her own. Lizzy, the older of the two girls, says she wants to be the one to end her father’s life before he turns. But she can’t do it.

“Lizzy, look at the flowers,” Mika says, holding her sister with their back to their dying father, both sobbing as Carol puts him out of his misery.

Upstairs, Rick, Daryl, Hershel, Bob, and “Dr. S,” (Subramanian, for the record), are examining the deceased. The walkers had no bites or scratches, but they were bleeding from their eyes, and ears, and mouths – much like the walker on the fence in last week’s episode.

Dr. S suggests it’s some violent form of flu, where the pressure builds up inside the victim, like a shaken can of soda and the top pops. “Only imagine your eyes, ears, nose and throat are the top.”

“Bugs like to run through close quarters,” Bob says. “It doesn’t get any closer than this.” Until they know exactly what it is, they all agree to quarantine anybody who was in D, or may have been exposed – which includes all of them.

Michonne got hurt as well. After swinging back into the prison, Carl was slow to close the gates. Several walkers got in, they beset Michonne as she dismounted, and she sprained her ankle before being rescued by Carl and Maggie.

While the others are dealing with the aftermath of the flu outbreak, Michonne is in C with Beth, who’s caring for Judith. Beth is asking about the people who died in D, if any kids died, but she doesn’t want to know the names. “All these widows, and orphans, but what do you call someone lost a child?” she says. “You think someone would’ve given that a name.”

Ding…ding…ding.

Beth is walking Judith (and singing an old Ramones tune as a lullaby), when the baby spits up on her. She brings Judith over to Michonne, to hold her while Beth changes. Michonne – who through everything we’ve seen of her has been absolutely fearless, nearly speechless, and always ready to roll – recoils, recoils from a baby, before reluctantly relenting. She holds Judith aloft, awkwardly, and it’s clear she’s afraid to even touch the infant.

And then, Michonne starts to cry. She stares into the baby’s eyes, and this mysterious warrior’s lip quivers, her eyes well up. She slowly cradles the baby against her, face to face, and Michonne cries, and cries. Danai Gurira, who plays Michonne, deserves credit for portraying the grief of what we now understand Michonne to be: a mother who lost her child. It’s a forceful moment.

Meanwhile, the mouse-fed walkers are threatening to break down the fences. (One of the best walkers effects yet: one presses his head through the fence, cutting a chain-link gash in his head.) Rick and Carl and Sasha and Daryl can’t kill them fast enough. Rick realizes they need to draw them off, and how to do it. He and Daryl drive out into the field, with Rick on a flatbed with his pigs. He cuts the pigs and throws them off, squealing, bait for the walkers. It works. But that’s pretty much the end of Rick the farmer. Before long, he’s torching the pen, handing Carl his gun, and holstering his own Colt Python. Rick, the Rick we knew, is back.

But that isn’t even the end of the horrors. Tyreese’s girlfriend Karen was coughing, so she was quarantined with the others in cell block A – death row. Tyreese visits with a clutch of flowers (“Look at the flowers, Lizzy”?), but finds only a trail of blood that runs from her room, down the hall, through a door, and into the yard.

Since the season four trailer hit the web, one of the big questions has been, what did Tyreese see? Now we find out. In the yard, two bodies lie, burned to death, burned beyond recognition. As Tyreese stares in horror, you can see the smoke, and hear the searing flesh.